1. Field of the Invention
The present invention relates to a method for reducing a smear effect of an image, and more particularly to a method for reducing a smear effect of a dynamic image.
2. Related Art
Most image sensors applied to digital cameras adopt charge-coupled devices (CCDs). When the image sensor senses a picture having a high brightness object, a smear effect occurs near the corresponding high brightness object. FIG. 1 is a schematic view of image data with a smear effect presented when an image sensor receives a picture having a high brightness object. Referring to FIG. 1, an image sensor 10 has a plurality of sensing pixels 12 arranged in arrays. Once the sensing pixels 12 sense the picture having the high brightness object, an object over-saturated pixel 14 and strip over-saturated pixels 16 are presented among the sensing pixels corresponding to the high brightness object. The object over-saturated pixel 14 and the strip over-saturated pixels 16 are the so-called smear effect.
In order to solve the smear effect problem, persons in the industry have proposed some solutions. For example, in US Patent No. 2006/0274173 A1, published on Dec. 7, 2006 (the patent family includes ROC Patent Application No. 200707327, WO/2006/123828, and so on), a digital camera comprising smear removal function is proposed. As known from the abstract, the following technique is disclosed. A horizontal evaluation data generation section calculates an average value of pixel signals in a vertical optical black region based on given pixel data in the horizontal optical black region and outputs the calculated average value to an evaluation section. A vertical evaluation data generation section calculates an average value of pixel signals in a vertical optical black region based on given pixel data in the vertical optical black region and outputs the calculated average value to the evaluation section. The evaluation section outputs a gain value according to the difference between the two sent average values to a computing section. A smear information memory stores pixel signals in a line in the vertical optical black region. The computing section multiplies the pixel data stored in the smear information memory by the sent gain value, and subtracts the multiplied pixel data from the pixel data imaged by the CCD. Therefore, a camera, a program, and a smear removing device are implemented, so as to change presence of smear removal or intensity of smear removal according to the smear generation state.
In addition, in US Patent Application No. 2007/0242145, published on Oct. 18, 2007 and entitled “Smear Reduction in CCD Images”, a technique of removing a smear effect in CCD images is provided. Rates of change of signals in the smeared area are taken as a basis (compared with a predefined limit) for detecting boundaries of the smeared area. After the boundaries are detected, the effective pixels corresponding to the smeared area are compensated by deriving from image pixels neighboring the detected smear or by interpolation.
In the above two methods for removing the smear effect, the smear removal process is merely performed on a single image, but cannot be performed on a part of continuous dynamic images. If the conventional smear removal method is directly used in the continuous dynamic images, the dynamic images may generate an unnatural side effect, such that the picture is too artifact.